In the first dojo I put my fot in, I saw the black belts taking turns in practising with each other on one hand, and picking the most inexperienced beginner on the mat on the other. This has been an important part of what aikido is to me for so long. When I come into environments where it does not work like this... I have had severe difficulties in adapting. I have not wanted to. Personally I'm trying to find a way to accept the choosy policy - not advocating it perhaps, but accepting it.
Also in aikido environments where you normally change partners every technique, this is often not done whem practising jo and bokken. Then you practise with the same partner the whole class, and suddenly people choose a lot more... I see the point in working for a longer time with the same partner. I have experienced the point of doing this in non-weapons aikido practise. Maybe you could see it as part of practise to learn how to get people interested in training with you, as part of hte human interaction-thing.
If Peter Goldsbury means what I think he does when he says that "the technique should work, no matter who is your partner" then there are aikido contexts where this statement does not hold true. I kind of wonder if being choosy is more prevalent in schools or styles where the concept of making the technique "work no matter what" is de-emphasized. I don't want it to be true, but nontheless have a feeling it is so.